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Subsurface drip irrigation improves water efficiency

The most productive cotton fields on the farm may not be the best bets for subsurface drip irrigation, according to Altus, Okla., farmers who have worked with underground irrigation systems for some 10 years.

“Drip pays off best on land that’s not conducive to furrow irrigation,” says Harold Worrell, who farms with his son Mitch in Jackson County, in the Southwestern corner of the state. He says land with “lower irrigation efficiency,” works well with drip systems.

“The water has to run downhill,” he says, “and land should be as level as possible. The key is to get yields equal to the rest of the farm.”

He says every acre in a properly installed drip system gets the same amount of water. “We even out distribution and improve water use efficiency,” he says. “Low spots in the fields will get more water and will hurt efficiency,” he says.

Perfectly level fields are not crucial. “Laser leveling is not necessary, but it’s nice to have,” Worrell says. “Old timers like me can look across a field and see where the water is moving and determine when we need to water. I can usually see when irrigation zones change.”

Worrell and his son currently have 2,000 acres of cotton in drip irrigation. “Mitch took a tour to California and saw drip irrigation there,” he says. “He came back and we installed a quarter section of drip in 1995. We’ve added a little more every year since.

“We got the tape installed after the cotton was up and then we got hailed out.” They replanted grain sorghum on the drip acreage. The following year’s crop performed well.

When hail took out more acreage in 1999, they installed drip on another 700 or 800 acres.

“We initiate irrigation based on the weather,” Worrell says. “That’s usually in July. And once we get started, we keep it going until September (Rainfall may allow them to shut down for brief periods in season.). We run drip irrigation a little longer than we do furrow. When we cut off the drip systems we’re ready to defoliate.”

They install drip on 150-acre blocks, with three 50-acre zones. “We set the system to water every four to six hours and we don’t run water on the same zone for too long or the moisture leaches out. Timing is automatic, three-tenths inch per acre every 24 hours.”

They add N-phuric to the water just before they change from one zone to another. “That takes about 15 minutes and keeps the lines clean. We pick up a little nitrogen from the acid but not much.”

Worrell says he and Mitch prefer to band most of their fertilizer instead of applying it through the system. “If we get rain, we’re not getting nitrogen to the cotton,” he says. “We band fertilizer on every other middle, where the tape is so when the cotton roots move to the water they pick up the nitrogen.”

They install tape on 80-inch spacing and plant on 40-inch rows. He says broadcasting fertilizer solid across the field wastes nutrients. “We can’t use it all,” he says. Banded fertilizer rates run 25 pounds to 30 pounds of phosphate instead of 50 pounds. They apply about 120 pounds of nitrogen, 2 pounds of zinc and 20 pounds to 30 pounds of sulfur.”

Maintenance has not posed severe difficulty. “Gophers can be trouble in sandy land,” Worrell says. “We have to fix the leaks and those are easy to find. Water bubbles up where the leak is.”

He says the oldest system on the farm, pushing 12 years, continues to perform well. “It still does a good job of irrigating cotton,” he says. “We’ve changed valves from electric to hydraulic and that works better.”

Worrell says a 2-inch rain in late March was “a life saver” as he and Mitch prepare to plant another crop. “The ground was as hard as I’ve ever seen it,” he says. “We tried to rip some land but we bent the bars on the plow. I’ve never seen conditions that dry and hard before.”

And that goes back a ways. Worrell has farmed this area since he graduated from Oklahoma State University in 1960.

Newer varieties have helped boost yields. He says FiberMax 960-B2R has performed well. Yields have been good and grades have been “excellent,” he says. “It has high strength, long staple and it doesn’t fall out. We pick it and it picks very well.”

He also likes the medium maturity.

Worrell says drip irrigation will help him and Mitch manage even in dry years.

“Precision water application is where drip irrigation really shines,” he says.

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